JPH05308768A - Stator yoke for stepping motor - Google Patents

Abstract

PURPOSE:To get a stator yoke which is easy to manufacture and can improve the yield rate of a product and gets off with a small number of parts and further is large in intrinsic electric resistance. CONSTITUTION:A can-type stator yoke 1 and a flat-type stator yoke 2 are manufactured by putting the composite powder between soft magnetic metallic powder and thermosetting synthetic resin powder into an ordinary injection molding machine, and heating it for molding. As a result, the manufacture processes becomes further less as compared with the conventional method by a sheet metal press, and besides the number of parts can be made less, and the cut down of the manufacture cost can be expected. Furthermore, since electric peculiar resistance is large, the calorific value also is small, and the current loss is little, and high speed rotation becomes possible. Besides, the tooth of the stator yoke is made in required shape, so it is highly reliable though small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepping motor, and more particularly to a stator yoke of a small stepping motor suitable for office automation equipment.

[0002]

2. Description of the Related Art A PM type two-phase stepping motor is shown in FIG.
11 and two pairs of flat stator yokes 1
2, 12 and a pair of two coils 13, 13 and one rotor 4.

By the way, the conventional stator yoke of the stepping motor is manufactured by pressing a sheet metal, which is a material, and its molding is performed as shown in FIG. 4 in the case of a flat type stator yoke. The blank disk is punched out from the plate (a), the blank disk is deep-drawn (b), the tooth part is punched out (c), and the tooth part is bent (d). In the case of York, the same process is performed.

[0004]

In the conventional method of manufacturing a stator yoke by press working, in the case of a small stepping motor, the teeth of the stator yoke become smaller, so the press tool also becomes smaller, which results in punching shots. The tool is frequently damaged by the impact at the time, and a defective stator yoke is often manufactured due to the tool damage, and the product yield is not good.

Further, in the case of press working, the sheet metal as a material for the stator yoke must be thin, and not only the plate thickness is restricted but also the small shape is restricted in the entire shape including the teeth.

Further, in the case of press working, as well as the can type stator yoke, two flat type stator yokes must be manufactured as shown by reference numerals 12 and 12 in FIG. In addition, in a stepping motor having a stake yoke manufactured by press working, the stator yoke also has a low specific electric resistance in terms of its performance. The loss is large.

In particular, as the rotation speed increases, the loss due to the eddy current increases, so that the electric power converted into the rotational energy of the input electric power decreases, and the torque during the high speed rotation decreases. Further, the eddy current becomes heat, and in the case of a small motor, the heat radiation area is small, so the temperature of the motor rises, and this temperature rise adversely affects the reliability of the motor.

Therefore, in order to withstand the heat generation, the insulating film of the coil is made to have excellent heat resistance, but the heat resistant insulating film is expensive, which increases the cost of the product.

As described above, in the stepping motor using the sheet-made stator yoke, the low specific electric resistance of the stator yoke has been a bottleneck for high-speed rotation and downsizing.

The present invention is easy to manufacture, and the product yield can be improved. Further, it is not necessary to manufacture two flat type stator yokes, one is sufficient, and the specific electric resistance is further improved. By using the stator yoke, which eliminates the drawbacks caused by the small size, the stepping motor can be rotated at high speed and downsized.

[0011]

A motor stator yoke according to the present invention is a composite powder material obtained by mixing a metal powder made of a soft magnetic material with a powder of a thermoplastic synthetic resin as a binder, and injection molding the same under heating. There is.

[0012]

Since the material used for the stator yoke for a motor according to the present invention is a composite powder material in which a powder of thermoplastic synthetic resin is mixed with a metal powder of a soft magnetic material, the synthetic resin powder is melted by heating. It serves as a binder of metal powder, and therefore, a stator yoke having a desired shape can be easily manufactured by injection molding.

In addition, the stator yoke manufactured in this manner has a relatively large specific electric resistance, so that the generation of eddy current is small, the heat generation is small, and the current loss is small, and the motor using this stator yoke is small. Enables high-speed rotation and miniaturization.

[0014]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 is an exploded perspective view of a stepping motor provided with a stator yoke according to the present invention, which is denoted by reference numerals 1 and 1.
Is a pair of two can type stator yokes made of two parts, 2 is a flat type stator yoke made of one part, 3 and 3 are coils, 4 is a rotor, 5 is a flange plate, and 1a and 2a are The tooth part of each stator yoke is shown.

In the present invention, the can type stator yokes 1, 1 and the flat type stator yoke 2 are made of a composite powder of a soft magnetic metal powder and a thermoplastic synthetic resin powder. Is an iron powder, and the thermoplastic synthetic resin is a polypropylene type.

A composite powder having the above composition is put into a usual injection molding machine and molded while being heated to manufacture a stator yoke having a required shape.

The stepping motor shown in FIG. 2 having the stator yoke injection-molded as described above and the stepping motor having the stator yoke molded by the conventional sheet metal press working (both stepping motors have a rotating shaft diameter of 8 mm). ) And each pull-in torque (Pull-in
When the torque) characteristic (starting characteristic) was measured, the results shown in FIG. 3 were obtained.

As can be understood from this characteristic diagram, in the conventional stepping motor of the stator yoke by the sheet metal press, the maximum starting frequency was close to 1500 Hz, but the maximum starting frequency of the motor equipped with the stator yoke of the present invention is 2000 Hz. It is near, and the frequency band has widened to 500 Hz.

[0020]

According to the present invention, since the stator yoke can be manufactured by injection, the number of manufacturing steps is much smaller than that of the conventional method using a sheet metal press, and the small size is required in the case of a small stepping motor. Even a toothed part can be molded into a required shape with high accuracy, defective products can be prevented as much as possible, and the product yield can be greatly improved.

Moreover, the flat type stator yoke does not have to be a pair of two parts, one part is sufficient, the number of parts can be reduced, and the manufacturing cost can be reduced.

Further, since the stator yoke of the present invention is made of a material in which soft magnetic metal powder is mixed with a synthetic resin material having a large electric insulation resistance as a binder, the stator yoke has a large electric specific resistance. Therefore, the generation of eddy current due to energization is small, therefore the amount of heat generation is small, the current loss is small, and it is possible to manufacture a stepping motor capable of high-speed rotation with high performance. However, there is an advantage that it is possible to provide a highly reliable stepping motor that is small in size.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a stepping motor including a stator yoke according to the present invention.

FIG. 2 is a partially cutaway perspective view of the motor.

FIG. 3 is a comparison diagram of pull-in torque characteristics of motors.

FIG. 4 is a process drawing of a case using a conventional sheet metal press method.

FIG. 5 is an exploded perspective view of a stepping motor including a conventional stator yoke.

[Explanation of symbols]

 1, 2 Stator yoke 1a, 2a Tooth part 3 Coil 4 Rotor 5 Flange plate

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Claims (1)

[Claims] 1. A stator yoke for a stepping motor, which is obtained by injection-molding a composite powder obtained by mixing a powder of a thermoplastic synthetic resin as a binder with a metal powder of a soft magnetic material under heating.